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Molecular Microbiology Mar 2021The type II secretion system (T2SS) is a multi-protein complex used by many bacteria to move substrates across their cell membrane. Substrates released into the... (Review)
Review
The type II secretion system (T2SS) is a multi-protein complex used by many bacteria to move substrates across their cell membrane. Substrates released into the environment serve as local and long-range effectors that promote nutrient acquisition, biofilm formation, and pathogenicity. In both animals and plants, the T2SS is increasingly recognized as a key driver of virulence. The T2SS spans the bacterial cell envelope and extrudes substrates through an outer membrane secretin channel using a pseudopilus. An inner membrane assembly platform and a cytoplasmic motor controls pseudopilus assembly. This microreview focuses on the structure and mechanism of the T2SS. Advances in cryo-electron microscopy are enabling increasingly elaborate sub-complexes to be resolved. However, key questions remain regarding the mechanism of pseudopilus extension and retraction, and how this is coupled with the choreography of the substrate moving through the secretion system. The T2SS is part of an ancient type IV filament superfamily that may have been present within the last universal common ancestor (LUCA). Overall, mechanistic principles that underlie T2SS function have implication for other closely related systems such as the type IV and tight adherence pilus systems.
Topics: Amino Acid Sequence; Animals; Bacterial Outer Membrane Proteins; Bacterial Physiological Phenomena; Bacterial Proteins; Cryoelectron Microscopy; Fimbriae, Bacterial; Humans; Models, Molecular; Protein Conformation; Secretin; Type II Secretion Systems; Virulence Factors
PubMed: 33283907
DOI: 10.1111/mmi.14664 -
Molecular Microbiology Aug 2005Twitching motility is a unique form of bacterial propulsion on solid surfaces associated with cycles of extension, tethering and retraction of type IV pili (T4P).... (Review)
Review
Twitching motility is a unique form of bacterial propulsion on solid surfaces associated with cycles of extension, tethering and retraction of type IV pili (T4P). Although investigations over the last two decades in a number of species have identified the majority of the genes involved in this process, we are still learning how these pili are assembled and the mechanics by which bacteria use T4P to drag themselves from one place to another. Among the puzzles that remain to be solved is the mechanism by which hydrolysis of ATP is coupled to pilus assembly and disassembly, and how the cell envelope structure is modified to accommodate the passage of the pilus through the periplasm. Unravelling of these and other enigmas in the T4P system will not only teach us more about these important colonization and virulence factors, but also help us to understand related processes such as type II secretion, which relies on a set of proteins homologous to those in the T4P system, and bacterial conjugation, involving retractable pili belonging to the F-like subgroup of the type IV secretion family. This review focuses on recent discoveries relating to the assembly and function of T4P in generation of twitching motility.
Topics: Adenosine Triphosphate; Fimbriae Proteins; Fimbriae, Bacterial; Genes, Bacterial; Gram-Negative Bacteria
PubMed: 16091031
DOI: 10.1111/j.1365-2958.2005.04703.x -
PloS One 2021Axenically cultured Liberibacter crescens (Lcr) is a closely related surrogate for uncultured plant pathogenic species of the genus Liberibacter, including 'Candidatus...
Axenically cultured Liberibacter crescens (Lcr) is a closely related surrogate for uncultured plant pathogenic species of the genus Liberibacter, including 'Candidatus L. asiaticus' (CLas) and 'Ca. L. solanacearum' (CLso). All Liberibacters encode a completely conserved gene repertoire for both flagella and Tad (Tight Adherence) pili and all are missing genes critical for nucleotide biosynthesis. Both flagellar swimming and Tad pilus-mediated twitching motility in Lcr were demonstrated for the first time. A role for Tad pili in the uptake of extracellular dsDNA for food in Liberibacters was suspected because both twitching and DNA uptake are impossible without repetitive pilus extension and retraction, and no genes encoding other pilus assemblages or mechanisms for DNA uptake were predicted to be even partially present in any of the 35 fully sequenced Liberibacter genomes. Insertional mutations of the Lcr Tad pilus genes cpaA, cpaB, cpaE, cpaF and tadC all displayed such severely reduced growth and viability that none could be complemented. A mutation affecting cpaF (motor ATPase) was further characterized and the strain displayed concomitant loss of twitching, viability and reduced periplasmic uptake of extracellular dsDNA. Mutations of comEC, encoding the inner membrane competence channel, had no effect on either motility or growth but completely abolished natural transformation in Lcr. The comEC mutation was restored by complementation using comEC from Lcr but not from CLas strain psy62 or CLso strain RS100, indicating that unlike Lcr, these pathogens were not naturally competent for transformation. This report provides the first evidence that the Liberibacter Tad pili are dynamic and essential for both motility and DNA uptake, thus extending their role beyond surface adherence.
Topics: Adenosine Triphosphatases; Amino Acid Sequence; Bacterial Proteins; Citrus; DNA, Bacterial; Fimbriae, Bacterial; Liberibacter; Mutagenesis, Site-Directed; Plant Diseases; Sequence Alignment
PubMed: 34644346
DOI: 10.1371/journal.pone.0258583 -
EcoSal Plus Feb 2019The type II secretion system (T2SS) delivers toxins and a range of hydrolytic enzymes, including proteases, lipases, and carbohydrate-active enzymes, to the cell surface... (Review)
Review
The type II secretion system (T2SS) delivers toxins and a range of hydrolytic enzymes, including proteases, lipases, and carbohydrate-active enzymes, to the cell surface or extracellular space of Gram-negative bacteria. Its contribution to survival of both extracellular and intracellular pathogens as well as environmental species of proteobacteria is evident. This dynamic, multicomponent machinery spans the entire cell envelope and consists of a cytoplasmic ATPase, several inner membrane proteins, a periplasmic pseudopilus, and a secretin pore embedded in the outer membrane. Despite the -envelope configuration of the T2S nanomachine, proteins to be secreted engage with the system first once they enter the periplasmic compartment via the Sec or TAT export system. Thus, the T2SS is specifically dedicated to their outer membrane translocation. The many sequence and structural similarities between the T2SS and type IV pili suggest a common origin and argue for a pilus-mediated mechanism of secretion. This minireview describes the structures, functions, and interactions of the individual T2SS components and the general architecture of the assembled T2SS machinery and briefly summarizes the transport and function of a growing list of T2SS exoproteins. Recent advances in cryo-electron microscopy, which have led to an increased understanding of the structure-function relationship of the secretin channel and the pseudopilus, are emphasized.
Topics: Adenosine Triphosphatases; Bacterial Proteins; Cryoelectron Microscopy; Fimbriae, Bacterial; Gram-Negative Bacteria; Membrane Proteins; Models, Molecular; Periplasm; Protein Binding; Secretin; Type II Secretion Systems
PubMed: 30767847
DOI: 10.1128/ecosalplus.ESP-0034-2018 -
Medical Microbiology and Immunology Jun 2020Type IV pili are versatile and highly flexible fibers formed on the surface of many Gram-negative and Gram-positive bacteria. Virulence and infection rate of several... (Review)
Review
Type IV pili are versatile and highly flexible fibers formed on the surface of many Gram-negative and Gram-positive bacteria. Virulence and infection rate of several pathogenic bacteria, such as Neisseria meningitidis and Pseudomonas aeruginosa, are strongly dependent on the presence of pili as they facilitate the adhesion of the bacteria to the host cell. Disruption of the interactions between the pili and the host cells by targeting proteins involved in this interaction could, therefore, be a treatment strategy. A type IV pilus is primarily composed of multiple copies of protein subunits called major pilins. Additional proteins, called minor pilins, are present in lower abundance, but are essential for the assembly of the pilus or for its specific functions. One class of minor pilins is required to initiate the formation of pili, and may form a complex similar to that identified in the related type II secretion system. Other, species-specific minor pilins in the type IV pilus system have been shown to promote additional functions such as DNA binding, aggregation and adherence. Here, we will review the structure and the function of the minor pilins from type IV pili.
Topics: Bacterial Adhesion; Fimbriae Proteins; Fimbriae, Bacterial; Host Microbial Interactions; Models, Molecular; Protein Conformation; Protein Multimerization; Virulence
PubMed: 31784891
DOI: 10.1007/s00430-019-00642-5 -
PLoS Pathogens Mar 2022The gram-negative bacterium Kingella kingae is a leading cause of osteoarticular infections in young children and initiates infection by colonizing the oropharynx....
The gram-negative bacterium Kingella kingae is a leading cause of osteoarticular infections in young children and initiates infection by colonizing the oropharynx. Adherence to respiratory epithelial cells represents an initial step in the process of K. kingae colonization and is mediated in part by type IV pili. In previous work, we observed that elimination of the K. kingae PilC1 and PilC2 pilus-associated proteins resulted in non-piliated organisms that were non-adherent, suggesting that PilC1 and PilC2 have a role in pilus biogenesis. To further define the functions of PilC1 and PilC2, in this study we eliminated the PilT retraction ATPase in the ΔpilC1ΔpilC2 mutant, thereby blocking pilus retraction and restoring piliation. The resulting strain was non-adherent in assays with cultured epithelial cells, supporting the possibility that PilC1 and PilC2 have adhesive activity. Consistent with this conclusion, purified PilC1 and PilC2 were capable of saturable binding to epithelial cells. Additional analysis revealed that PilC1 but not PilC2 also mediated adherence to selected extracellular matrix proteins, underscoring the differential binding specificity of these adhesins. Examination of deletion constructs and purified PilC1 and PilC2 fragments localized adhesive activity to the N-terminal region of both PilC1 and PilC2. The deletion constructs also localized the twitching motility property to the N-terminal region of these proteins. In contrast, the deletion constructs established that the pilus biogenesis function of PilC1 and PilC2 resides in the C-terminal region of these proteins. Taken together, these results provide definitive evidence that PilC1 and PilC2 are adhesins and localize adhesive activity and twitching motility to the N-terminal domain and biogenesis to the C-terminal domain.
Topics: Adhesins, Bacterial; Adhesives; Bacterial Adhesion; Bacterial Proteins; Child; Child, Preschool; DNA; Fimbriae Proteins; Fimbriae, Bacterial; Humans; Kingella kingae
PubMed: 35353876
DOI: 10.1371/journal.ppat.1010440 -
Structure (London, England : 1993) May 2023Bacterial adhesion pili are key virulence factors that mediate host-pathogen interactions in diverse epithelial environments. Deploying a multimodal approach, we probed...
Bacterial adhesion pili are key virulence factors that mediate host-pathogen interactions in diverse epithelial environments. Deploying a multimodal approach, we probed the structural basis underpinning the biophysical properties of pili originating from enterotoxigenic (ETEC) and uropathogenic bacteria. Using cryo-electron microscopy we solved the structures of three vaccine target pili from ETEC bacteria, CFA/I, CS17, and CS20. Pairing these and previous pilus structures with force spectroscopy and steered molecular dynamics simulations, we find a strong correlation between subunit-subunit interaction energies and the force required for pilus unwinding, irrespective of genetic similarity. Pili integrate three structural solutions for stabilizing their assemblies: layer-to-layer interactions, N-terminal interactions to distant subunits, and extended loop interactions from adjacent subunits. Tuning of these structural solutions alters the biophysical properties of pili and promotes the superelastic behavior that is essential for sustained bacterial attachment.
Topics: Fimbriae Proteins; Bacterial Adhesion; Cryoelectron Microscopy; Fimbriae, Bacterial
PubMed: 37001523
DOI: 10.1016/j.str.2023.03.005 -
Frontiers in Cellular and Infection... 2021The remarkable genomic plasticity of largely depends on its ability to undergo natural genetic transformation. To take up extracellular DNA, assembles competence pili...
The remarkable genomic plasticity of largely depends on its ability to undergo natural genetic transformation. To take up extracellular DNA, assembles competence pili composed of the major pilin ComGC. In addition to ComGC, four minor pilins ComGD, E, F, and G are expressed during bacterial competence, but their role in pilus biogenesis and transformation is unknown. Here, using a combination of protein-protein interaction assays we show that all four proteins can directly interact with each other. Pneumococcal ComGG stabilizes the minor pilin ComGD and ComGF and can interact with and stabilize the major pilin ComGC, thus, deletion of ComGG abolishes competence pilus assembly. We further demonstrate that minor pilins are present in sheared pili fractions and find ComGF to be incorporated along the competence pilus by immunofluorescence and electron microscopy. Finally, mutants of the invariant Glu5 residue (E5), ComGD or ComGE, but not ComGF, were severely impaired in pilus formation and function. Together, our results suggest that ComGG, lacking E5, is essential for competence pilus assembly and function, and plays a central role in connecting the pneumococcal minor pilins to ComGC.
Topics: Fimbriae Proteins; Fimbriae, Bacterial; Streptococcus pneumoniae
PubMed: 35004361
DOI: 10.3389/fcimb.2021.808601 -
Philosophical Transactions of the Royal... Apr 2012Up to eight different types of secretion systems, and several more subtypes, have been described in Gram-negative bacteria. Here, we focus on the diversity and assembly... (Review)
Review
Up to eight different types of secretion systems, and several more subtypes, have been described in Gram-negative bacteria. Here, we focus on the diversity and assembly mechanism of one of the best-studied secretion systems, the widespread chaperone-usher pathway known to assemble and secrete adhesive surface structures, called pili or fimbriae, which play essential roles in targeting bacterial pathogens to the host.
Topics: Adhesins, Escherichia coli; Bacterial Secretion Systems; Fimbriae Proteins; Fimbriae, Bacterial; Genetic Complementation Test; Genetic Variation; Gram-Negative Bacteria; Host-Pathogen Interactions; Molecular Chaperones; Multigene Family; Multiprotein Complexes; Protein Structure, Tertiary; Receptors, Immunologic
PubMed: 22411982
DOI: 10.1098/rstb.2011.0206 -
Acta Crystallographica. Section F,... Aug 2021Adhesion to host surfaces for bacterial survival and colonization involves a variety of molecular mechanisms. Ligilactobacillus ruminis, a strict anaerobe and gut...
Adhesion to host surfaces for bacterial survival and colonization involves a variety of molecular mechanisms. Ligilactobacillus ruminis, a strict anaerobe and gut autochthonous (indigenous) commensal, relies on sortase-dependent pili (LrpCBA) for adherence to the intestinal inner walls, thereby withstanding luminal content flow. Here, the LrpCBA pilus is a promiscuous binder to gut collagen, fibronectin and epithelial cells. Structurally, the LrpCBA pilus displays a representative hetero-oligomeric arrangement and consists of three types of pilin subunit, each with its own location and function, i.e. tip LrpC for adhesion, basal LrpB for anchoring and backbone LrpA for length. To provide further structural insights into the assembly, anchoring and functional mechanisms of sortase-dependent pili, each of the L. ruminis pilus proteins was produced recombinantly for crystallization and X-ray diffraction analysis. Crystals of LrpC, LrpB, LrpA and truncated LrpA generated by limited proteolysis were obtained and diffracted to resolutions of 3.0, 1.5, 2.2 and 1.4 Å, respectively. Anomalous data were also collected from crystals of selenomethionine-substituted LrpC and an iodide derivative of truncated LrpA. Successful strategies for protein production, crystallization and derivatization are reported.
Topics: Amino Acid Sequence; Crystallization; Crystallography, X-Ray; Fimbriae, Bacterial; Gastrointestinal Microbiome; Lactobacillus; X-Ray Diffraction
PubMed: 34341189
DOI: 10.1107/S2053230X21007263